N & S America civilizations were quite fragmented, as well as African ones.
Not having cows and pigs and horses is a huge disadvantage.
They did have moose and deer and llamas and bears and goats and bison. I don't know if there's any proof they can't be domesticated given enough generations, time and patience. Wolves and foxes can be domesticated.
The Finns domesticated reindeer.
Lack of plough animals doesn't extinguish the human creative spirit, it just slows it down a lot.
It is curious why bison were not domesticated. I did a bit of research and could not find a clear reason (some suggestions that maybe Aurochs lived in forests and smaller herds, and that may have made them easier to domesticate... but that seems weak).
I'm wondering how much is due to what I'd call the Harari perspective, in Homo Deus - that Eurasians also invented the "god-centric worldview package" that shifted the view of the world from a more animistic perspective (where all beings share the world and so treating animals in the absolutely horrific ways that domestication and agriculture requires is just unthinkable, since they are seen as other beings sharing the world with us) to the "gods and humans" perspective (where god created humanity, and then every other being is just subservient and lacks a soul and therefore can be exploited, murdered, treated like goods, etc).
Mesoamerican religions, despite all the human sacrifice, did see animals and plants as intrinsically valuable and spiritually significant. Native Americans in the North definitely did that too (and they had more exposure to bisons). That would perhaps have led them not to seek to domesticate animals.
It is curious (to me) that no culture emerged that even tried, though (that culture would likely have outcompeted everyone else).
Jarrad had to make North Africans "honary europeans" to make,e his theories work
It has a huge east west extent
https://images.newscientist.com/wp-content/uploads/2018/08/1...
https://upload.wikimedia.org/wikipedia/commons/thumb/6/61/Eq...
It has North South as well
North Africa is included in Diamond's Mediterranean exchange zone. And that zone extends out of Europe to the Fertile Crescent, at the very least, and arguably to India and China as well. Africa's two zones are separated by the largest and most inhospitable desert on earth. There is no advantage in having two.
That is in fact the core idea Diamond is expressing.
Domesticatable flora and fauna from a huge and ecologically diverse geographic region were easily diffused around the entire zone. The difficulty of migrating horses or sheep across the Sahara, or turkeys and llamas across the Darien Gap, is much much higher. Sub-Saharan Africa started with few large animals suitable for domestication, and importing new ones was comparably difficult.